The invention relates to techniques for determining the haemolysis of a blood sample and devices therefore.
So-called oximeters are used for determining constituents of blood samples. Here it concerns optical measuring devices with which total haemoglobin (tHb), haemoglobin derivates such as oxyhaemoglobin (O2Hb), carboxyhaemoglobin (COHb), methaemoglobin (MetHb) and the degradation product bilirubin are determined. These parameters are photometrically determined on the basis of the Lambert-Beer law. For this, usually the additive absorption of the individual components for several discrete wave lengths in the visible area is measured, for example between 459 nm and 666 nm. The determined measuring values form an over-determined linear equation system, which can be solved by means of a multi-linear regression to determine the concentrations concerned.
Measurement of the haemoglobin derivates takes place in the haemolysate, i.e., a haemolysed blood sample. This means that all dispersive corpuscular blood components such as erythrocytes and similar are completely destroyed as far as possible before the optical measuring value recording; that means haemolysed. The haemolysis of the blood cells takes place typically in that ultrasound is applied to the blood sample. On the basis of the medium homogenised in this manner, the Lambert-Beer law can be taken for actual determination of the concentration of the components which describes the constant weakening of light irradiated into the blood sample to be examined along its path through the blood sample.
In non-haemolysed condition, blood represents, in optical respect, a cloudy “colourful” particle-containing medium. Any light cast is weakened and dispersed depending on the wave length. Dispersal of the light takes place primarily on the cells located in the blood. The high degree of absorption of the short-wave blue light and the relatively low absorption of the red/infrared light through the blood emphasise the characteristic red colour of the blood. The various blood components influence the light absorption in characteristic wave-length ranges. The water contained in the blood absorbs infrared light above 1000 nm very intensively while proteins and haemoglobin preferably absorb in the green and blue spectral area.
In the non-haemolysed whole blood there is, alongside the absorption, dispersion and diffraction of the incidental light on the particles contained within it (above all on the cellular blood components). Due to the complexity of the dispersion method, conditioned above all by the form-conditioned high anisotropism and the bi-conclave cross-section and the variance of form of the erythrocytes, there is no analytically simply presentable connection between the concentration of the materials dissolved in the blood and the weakening of the light detected. To be able to carry out reproducible and informative optical measurements, the blood is therefore haemolysed.
When the blood has been completely haemolysed and if, in addition, all dispersing cell fragments have been removed, the light falling on the blood sample in the photometric examination is ideally exclusively absorbed by the components contained within it. The Lambert-Beer law can then be used for the determination of the concentration of the blood components.
Haemolysis is thus a significant prerequisite for subsequent photometric examination of blood samples. There is therefore a need for techniques for the determination of the haemolysis itself, in particular to create defined output conditions for subsequent examination of the haemolysed blood sample and thus to improve the accuracy and reproducibility of analytical examinations.